An azobenzene functionalized covalent organic framework material and a method of preparing the same

Abstract

The application discloses an azobenzene functionalized covalent organic framework material and a preparation method thereof, and belongs to the field of functional polymer materials. Azobenzene groups in the azobenzene functionalized covalent organic framework material change from trans to cis isomerization under the action of ultraviolet light. The specific surface area change rate of the azobenzene functionalized covalent organic framework material is 12% to 20% before and after 365 nm ultraviolet light irradiation, the pore volume change rate is 15% to 40%, and the pore size change rate is 7% to 10%. The azobenzene functionalized covalent organic framework material has high crystallinity, high stability and high specific surface area, and can spontaneously adjust a pore environment under ultraviolet light irradiation.

Description

Technical Field

[0001] This application relates to the field of functional polymer materials technology, specifically to an azobenzene functionalized covalent organic framework material and its preparation method. Background Technology

[0002] Porous materials are a class of advanced functional materials with a large number of pores. Based on pore size, they can be divided into three categories: micropores (≤ 2 nm), mesopores (2-50 nm), and macropores (≥ 50 nm). Their highly ordered structure and customizable pores can accommodate guest substances such as atoms, ions, or molecules to fill the pores. This characteristic makes them promising for a wide range of applications in specific fields such as gas storage and separation, catalysis, proton conduction, and sensing (Chem. Soc. Rev., 2020, 49, 4360-4404; Angew. Chem. Int. Ed., 2023, 62, e202216724). Among numerous porous materials, covalent organic frameworks (COFs) are a class of crystalline porous polymer materials with two-dimensional or three-dimensional extended network structures. With their unique periodic structure, excellent thermal stability, high specific surface area, high pore volume and low density, they have been widely used in gas adsorption and storage, membrane separation, chemical sensing, catalysis and optoelectronics (Chem. Soc. Rev., 2020, 49, 708-735; Chem. Rev., 2020, 120, 16, 8814-8933).

[0003] Covalently packed free radicals (COFs) are a class of porous crystalline polymers with predictable structures, low density, and high covalent bond strength. They exhibit high flexibility in molecular design, allowing for precise assembly at the atomic level by controlling the shape, size, and topology of the pores through monomer structure modulation. The pore environment of COFs (such as pore size, shape, and chemical properties) and the stability of their crystal structure play a crucial role in their application performance (J. Clean. Prod., 2020, 277, 123360; Chem. Soc. Rev., 2019, 48, 3903-3945). However, currently reported functionalized COFs still have many drawbacks: most COFs are linked by traditional reversible covalent bonds (such as imine bonds), resulting in insufficient structural stability and potential framework destruction during application; COFs mostly exist in the form of microcrystalline powders, making it difficult to precisely control the size and shape of the crystals; furthermore, once synthesized, the pore size of COFs is usually fixed, lacking adjustability. These problems severely limit their practical applications. Therefore, developing simple and efficient preparation methods to obtain COFs with high stability, high crystallinity, and high specific surface area, and to achieve intelligent control of their pore environment, remains a current research hotspot and challenge in this field. Summary of the Invention

[0004] Based on this, this application provides an azobenzene functionalized covalent organic framework material with high crystallinity, high stability and high specific surface area, and can spontaneously adjust the pore environment under ultraviolet light irradiation.

[0005] An azobenzene-functionalized covalent organic framework material has the following structural formula: , The azophenyl group in the structural formula undergoes a trans-to-cis isomerization change under ultraviolet light.

[0006] In the azobenzene functionalized covalent organic framework material (Azo-COF) provided in this application, the thiazole-linked Azo-COF solves the instability problem of conventional imine-linked COF, enabling it to be used in harsh environments. At the same time, Azo-COF has good crystallinity, and the regularly stacked pore structure is conducive to the smooth realization of material transport and stimulus response functions.

[0007] The azobenzene-functionalized covalent organic framework material provided in this application exhibits UV responsiveness. Under UV irradiation, the azobenzene functional groups within the Azo-COF pores undergo a trans-to-cis isomerization transformation. After the UV light is removed, heating to 110-130°C causes the azobenzene functional groups within the Azo-COF pores to undergo a cis-to-trans isomerization transformation. Simultaneously, the suspended azobenzene groups within the pores have sufficient space to undergo reversible trans-to-cis isomerization transformations. Therefore, the surface wettability, specific surface area, and pore environment (including pore volume and pore size) of Azo-COF can be controlled using UV light, demonstrating its great potential as a photoresponsive smart porous material.

[0008] Several alternative methods are provided below, but they are not intended as additional limitations on the overall solution above. They are merely further additions or optimizations. Provided there are no technical or logical contradictions, each alternative method can be combined individually with respect to the overall solution above, or multiple alternative methods can be combined with each other.

[0009] Optionally, the specific surface area of ​​the azobenzene functionalized covalent organic framework material changes by 12% to 20% before and after irradiation with 365nm ultraviolet light.

[0010] Optionally, the azobenzene functionalized covalent organic framework material exhibits a pore volume change rate of 15%~40% and a pore diameter change rate of 7%~10% before and after 365nm ultraviolet irradiation.

[0011] This application also provides a method for preparing the azobenzene functionalized covalent organic framework material, comprising the following steps: 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine (CAS: 2092028-48-1), elemental sulfur and a mixed solvent were mixed evenly, and then heated under catalytic conditions in a sealed liquid nitrogen cryogenic vacuum environment. After post-treatment, the azobenzene functionalized covalent organic framework material was obtained. The mixed solvent is composed of dimethyl sulfoxide, o-dichlorobenzene and n-butanol.

[0012] This application employs a multi-component one-pot method to prepare the aforementioned azobenzene functionalized covalent organic framework material. The choice of mixed solvent has a significant impact on the synthesis of the azobenzene functionalized covalent organic framework material. The choice of solvent affects the solubility of the reaction system. Therefore, the reaction rate, crystal nucleation, growth rate, structural self-healing, and stacking mode can be adjusted by the choice of solvent, which will ultimately significantly affect the crystallinity, porosity, and reaction yield of the azobenzene functionalized covalent organic framework material.

[0013] The raw materials (excluding the catalyst) are ultrasonically mixed until homogeneous. The catalyst is then added, and the mixture is sealed after at least three freeze-evacuation-thawing cycles. Finally, the mixture is heated to carry out the reaction.

[0014] The post-processing includes sequentially filtering to collect the product, washing with anhydrous tetrahydrofuran and acetone, purifying with an anhydrous tetrahydrofuran and acetone Soxhlet extractor for at least 24 hours, and vacuum drying.

[0015] The structural formula of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde is as follows:

[0016] The structural formula of 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine is as follows:

[0017] Optionally, in the mixed solvent, the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:15~25:50~63.

[0018] Optionally, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine, and elemental sulfur is 1:2~4:4~8.

[0019] Optionally, the ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde to the mixed solvent is 0.015 mmol to 0.020 mmol: 1 mL.

[0020] Optionally, the catalyst is an aqueous solution of acetic acid. The aqueous solution of acetic acid has a concentration of 6 mol / L, and the volume ratio of the aqueous solution of acetic acid to dimethyl sulfoxide is 2:1.

[0021] Optionally, the reaction temperature for the sealed heating reaction is 100~150℃.

[0022] Optionally, the reaction time for the sealed heating reaction is 3 to 5 days.

[0023] Compared with the prior art, the beneficial effects of this application are: (1) The raw materials for the reaction are widely available and can be obtained from existing commercial channels. The cost is low and the synthesis method is simple and easy to implement.

[0024] (2) The thiazole bond-linked COF solves the problem of instability of conventional imine bond COF, and provides the possibility for the application of COF in harsh environments.

[0025] (3) The synthesized Azo-COF has good crystallinity, and the regularly stacked pore structure is conducive to the smooth realization of material transport and stimulus response functions.

[0026] (4) By irradiating with ultraviolet light, the azophenyl groups suspended in the pores have enough space to carry out reversible trans-cis isomerization transformation, realizing the light-induced regulation of COF surface wettability and pore environment, showing great potential as a photoresponsive smart porous material. Attached Figure Description

[0027] Figure 1 It is the solid-state Azo-COF prepared in Example 1 of this application. 13 CP-MAS NMR spectrum; Figure 2 This is the FT-IR spectrum of the Azo-COF prepared in Example 1 of this application; Figure 3 In the image, (a) is a SEM image of Azo-COF prepared in Example 1 of this application, and (b) and (c) are TEM images of Azo-COF prepared in Example 1 of this application, where (c) is an enlarged view of the dashed box in (b). Figure 4 This is the PXRD pattern of Azo-COF prepared in Example 1 of this application; Figure 5 This is the TGA curve of Azo-COF prepared in Example 1 of this application; Figure 6In the table, (a) is the PXRD spectrum of Azo-COF prepared in Example 1 of this application after being treated in various solvents for 3 days, and (b) is the residual weight percentage bar chart of Azo-COF prepared in Example 1 of this application after being treated in various solvents for 3 days. Figure 7 In the image, (a) shows the UV-Vis spectra of the ethanol solution of Azo-COF prepared in Example 1 of this application after being irradiated with 365nm ultraviolet light for different times, and (b) is an enlarged view of the dashed box in (a). Figure 8 This is a graph showing the change in surface wettability of Azo-COF prepared in Example 1 of this application before and after ultraviolet light irradiation; Figure 9 In the table, (a) is the N2 adsorption and desorption isotherm curve of Azo-COF prepared in Example 1 of this application before and after ultraviolet light irradiation, and (b) is the pore size distribution curve of Azo-COF prepared in Example 1 of this application before and after ultraviolet light irradiation. Figure 10 In the diagram, (a) shows the bandgap energy change of the Azo-COF / CNT composite material prepared in Example 1 of this application before and after ultraviolet light irradiation, and (b) shows the conductivity of the Azo-COF / CNT composite material prepared in Example 1 of this application before and after ultraviolet light irradiation. Figure 11 This is a graph showing the percentage contribution of the Azo-COF / CNT composite material (Azo-COF / CNT) prepared in Example 1 of this application to the capacitance-controlled charge storage before and after ultraviolet light irradiation; Figure 12 In the figure, (a) is a comparison of the CV curves of the Azo-COF / CNT composite material prepared in Example 1 of this application before and after ultraviolet light irradiation, and (b) is the CV cycle curve of cis-Azo-COF / CNT at a scan rate of 1mV / s. Detailed Implementation

[0028] The present application will be further described below with reference to the accompanying drawings and specific embodiments. The examples given are only for explaining the present application and do not limit the present application to the scope of the embodiments described.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0030] The characterization methods involved in the following embodiments are as follows: The structure of Azo-COF was determined using solid-state methods. 13CP-MAS NMR and FT-IR were measured on a Bruker AVANCII NMR500 superconducting nuclear magnetic resonance spectrometer and a Nicolet 5700 infrared spectrometer, respectively.

[0031] The morphology of Azo-COF was characterized using a Zeiss SEM-4800 scanning electron microscope (Germany) and JEOL JEM-1400 and JEM-2100 transmission electron microscopes (Japan).

[0032] The crystal structure characterization of Azo-COF was performed on a Rigaku D / max2550VB PC under the following conditions: voltage 40 kV, current 40 mA, CuK radiation current (λ = 1.5406 Å, step size 0.0020º), radiation entrance slit 2 mm, and angle range 1.5º ~ 30º.

[0033] The thermal decomposition properties of Azo-COF were characterized under a nitrogen atmosphere using thermogravimetric-chromatographic-mass spectrometry (TGA) at a heating rate of 10 °C / min and a temperature range of 25 ~ 1000 °C.

[0034] The photoresponsiveness of the azophenyl group in Azo-COF was characterized using a Shimadzu UV-2600 spectrometer.

[0035] The permanent porosity of Azo-COF was characterized at 77 K using an ASAP 2020HD88 surface area and pore size analyzer. The samples were dried at 120 °C for 8 h before measurement.

[0036] The electrochemical performance testing of Azo-COF / CNT included: obtaining the band gap by measuring the solid-state ultraviolet absorption spectrum, measuring the resistance using a four-probe resistor to obtain the conductivity, and obtaining the electrochemical reaction kinetics using cyclic voltammetry. The specific algorithms are as follows: The band gap is obtained by measuring the ultraviolet absorption spectrum of a solid, and the calculation formula is as follows: (Ahν) 1 / n = (hν- E g ) In the formula, hν is the photon energy, and h is Planck's constant (h ≈ 4.13567 × 10⁻⁶). -15 eV·s), where ν is the frequency of the incident photon (ν = cλ⁻¹, where c is the speed of light, c ≈ 3 × 10⁻¹⁰). 8 m / s; λ is the wavelength of the incident light. E gLet A be the bandgap of the semiconductor material, A be the ultraviolet absorbance, and n be related to the type of semiconductor material. When the semiconductor material has a direct bandgap, n = 0.5; when the semiconductor material has an indirect bandgap, n = 2. (Ahν) 1 / n Plotting hν as the ordinate and hν as the abscissa, we perform a linear fit on the approximate straight line portion. The intercept of the linear equation on the x-axis is the desired bandgap width.

[0037] The resistance of the material was measured using a four-probe resistance measurement method. A smooth Azo-COF / CNT composite sample was placed on an insulating substrate, and four probes were arranged at a specific spacing on the sample. The current and voltage values ​​were recorded. Based on the measured current and voltage, and the sample dimensions, the conductivity (σ) was calculated. σ = L / (RA) In the formula, L is the sample length, R is the resistance, and A is the cross-sectional area.

[0038] Cyclic voltammetry (CV) was performed on an electrochemical workstation (Chenhua, Shanghai). The test voltage window was 0.01–3 V, and the scan rates were set to 1 mV / s, 2 mV / s, 5 mV / s, and 10 mV / s. The electrochemical reaction kinetics of the Azo-COF / CNT material were studied by scanning CV at different rates. The charge storage properties were investigated using the power-law formula. i = aνb in i and ν These correspond to peak current and scan rate, respectively. a and b It is a variable constant. b A value close to 0.5 indicates a diffusion-controlled process; conversely, b A value close to 1 indicates a capacitor-controlled process.

[0039] The diffusion and capacitance contributions can be calculated using the following equations: i = k 1 ν + k2 ν 0.5 in i Represents current. k 1 ν k2 represents the current contributed by the capacitive process. ν 0.5 This represents the current contributed by the diffusion process. ν This represents the scan rate.

[0040] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0041] Example 1 A method for preparing an azobenzene-functionalized covalent organic framework material includes the following steps: (1) Add 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (30.9 mg, 0.05 mmol), 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine (36.4 mg, 0.10 mmol), cyclooctasulfide (76.8 mg, 0.30 mmol), dimethyl sulfoxide (150 μL), o-dichlorobenzene (712.5 μL), and n-butanol (2137.5 μL) to a heat-resistant Pyrex glass tube and sonicate to dissolve for about 5 min. Then add 0.3 mL of 6M acetic acid aqueous solution to the glass tube, and seal after three freeze-evacuation-thawing cycles. At this point, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine and cyclooctasulfide is 1:2:6, and the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:19:57.

[0042] (2) The sealed tube was heated in a 120°C forced-air drying oven for 4 days. The precipitate was collected by filtration and washed three times each with anhydrous tetrahydrofuran (THF) and acetone. Then, it was purified by a Soxhlet extractor of tetrahydrofuran and acetone for 24 hours. After vacuum drying, a solid powder was obtained, which is the azobenzene functionalized covalent organic framework material (i.e., Azo-COF). The yield of this example was 78.3%. PXRD test showed that the Azo-COF prepared in this example had good crystallinity, and its BET specific surface area was measured to be 451.95 m². 2 / g.

[0043] The properties of the azobenzene-functionalized covalent organic framework material obtained in this embodiment were characterized, and the results are shown in [reference needed]. Figures 1-6 As shown.

[0044] Figure 1 solid state 13CP-MAS NMR spectra showed that Azo-COF exhibited signal peaks at 120–132 ppm caused by carbon atoms on the aromatic benzene ring. Peaks corresponding to the thiazole carbon (SC=N) on the thiazole ring and the adjacent phenyl carbon of the thiazole ring appeared at 166 and 157 ppm, respectively. Furthermore, elemental analysis of Azo-COF showed carbon, nitrogen, and hydrogen contents of 76.93%, 7.41%, and 4.00%, respectively, which are close to their theoretical values ​​(C: 79.20%, N: 7.70%, H: 4.25%).

[0045] Figure 2 The FT-IR spectrum shows that at 1602 cm⁻¹ -1 The appearance of a C=N stretching vibration peak of the thiazole ring at 1240 cm⁻¹ indicates the presence of a thiazole bond in Azo-COF. Azo-COF exhibits a peak at 1240 cm⁻¹. -1 and 690 cm -1 The presence of a characteristic stretching vibration peak of an azo group (N=N) at the location proves that Azo-COF contains an azophenyl group.

[0046] Figure 3 SEM and TEM images show that Azo-COF has a continuous hollow rod-like structure with a diameter of 0.70–1.90 μm. From the magnified images, a 2.78 nm periodically oriented lattice corresponding to the (100) plane can be clearly observed, which is consistent with the 2.8 nm in-plane channels in the AA stacked structure. The clearly visible lattice and layered structure demonstrate the good crystallinity of Azo-COF.

[0047] Figure 4 The PXRD pattern (powder X-ray diffraction pattern) shows that Azo-COF exhibits a sharp (100) plane diffraction peak at approximately 2.71º, confirming the synthesis of a highly crystalline COF material. Diffraction peaks corresponding to the (110), (220), (240), (440), and (001) planes appear at 5.68º, 6.81º, 14.27º, and 24.75º, respectively. Among them, the 001 peak corresponds to the π-π stacking spacing (3.6 Å) between adjacent layers. By comparison, the PXRD pattern generated by the AA stacking mode is consistent with the experimental observation, and the Pawley optimization result is in good agreement with the experimentally observed pattern, with negligible differences (Rwp = 5.36% and Rp = 4.05%), confirming that the synthesized Azo-COF has an AA stacking structure. The cell parameters established by Pawley optimization are a = 45.39 Å, b = 44.71 Å, c = 3.79 Å, α = β = γ = 90°.

[0048] Figure 5The TGA curves show that the weight loss rate of Azo-COF is less than 7% in the temperature range of 25 ~ 400 °C. This is due to the weight loss caused by the evaporation of adsorbed water and residual solvent in the COF pores. However, after 410 °C, the framework begins to collapse, and significant weight loss (sharp tilt) begins to appear, indicating that Azo-COF has good thermal stability in a nitrogen environment and a decomposition temperature above 400 °C.

[0049] Figure 6 The chemical stability of Azo-COF was evaluated by immersing it in boiling water, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), 12.0 M concentrated HCl aqueous solution, 12.0 M NaOH aqueous solution, and 1.0 M sodium borohydride aqueous solution for 3 days. The structural integrity of the Azo-COF powder after solvent immersion was studied by PXRD and mass loss. Even under harsh conditions (strong acid or strong base), the PXRD curve of Azo-COF did not show significant changes compared with the untreated state, and the residual weight percentage of the powder also did not change significantly, being 94.0% (boiling water), 98.0% (THF), 94.0% (DMF), 94.2% (12.0 M NaOH), 98.0% (12.0 M HCl), and 93.9% (1.0 M NaBH4), respectively. This indicates that the thiazole-bonded Azo-COF does not show significant loss of crystallinity even under harsh conditions and has good structural stability.

[0050] An ethanol solution of Azo-COF (0.05 mg / mL) was irradiated under 365 nm ultraviolet light for 15 min, and the changes in its absorption peak were monitored by UV-Vis spectroscopy to prove the trans-cis isomerization transformation of the azophenyl group in the pores of Azo-COF.

[0051] Figure 7 The UV absorption spectrum of Azo-COF in ethanol solution is shown as a function of 365 nm UV irradiation time. Azo-COF exhibits an absorption peak at 314 nm corresponding to the trans-azobenzene unit's π-π* transition. With increasing 365 nm UV irradiation time, the intensity of the π-π* transition absorption band initially appearing near 314 nm gradually decreases, while the absorption peak at 435 nm corresponding to the n-π* transition slowly increases until it remains constant after 15 min of UV irradiation. At this point, the proportion of the cis isomer is approximately 53.95%, indicating that the azobenzene group within the pores of Azo-COF exhibits good photoisomerization behavior.

[0052] Azo-COF solid powder was exposed to ultraviolet light for 30 min, and the surface wettability of Azo-COF before and after the light exposure was compared.

[0053] Figure 8 The changes in surface wettability of Azo-COF before and after UV irradiation were shown. After 30 min of UV irradiation, the contact angle of Azo-COF decreased from 143.8º to 115.4º, indicating that some azobenzene in the pores of Azo-COF underwent a transformation from the trans isomer to the cis isomer, which reduced the dipole moment and thus increased wettability.

[0054] Azo-COF solid powder was exposed to ultraviolet light for 30 min, and the specific surface area, pore volume and pore size of Azo-COF before and after irradiation were compared by nitrogen adsorption-desorption isotherms.

[0055] Figure 9 The N2 adsorption and desorption isotherms and pore size distribution curves of Azo-COF before and after UV irradiation are shown. After exposing the Azo-COF solid powder to UV light for 30 min, the measured specific surface area increased from 451.95 m² / s². 2 / g increased to 539.6 m 2 / g, pore volume from 0.25 cm³ 3 / g increased to 0.33 cm 3 / g, the pore size increased from 21.62 Å to 23.41 Å. This is because under ultraviolet light irradiation, the trans-azobenzene unit transforms into an in-plane bent cis configuration, which generates more free space adsorbed N2 molecules, thus increasing the specific surface area, pore volume, and pore size.

[0056] Example 2 A method for preparing an azobenzene-functionalized covalent organic framework material includes the following steps: (1) Add 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (31.0 mg, 0.05 mmol), 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine (54.7 mg, 0.15 mmol), cyclooctasulfide (64.1 mg, 0.25 mmol), dimethyl sulfoxide (150 μL), o-dichlorobenzene (633.3 μL), and n-butanol (2216.7 μL) to a heat-resistant Pyrex glass tube and sonicate to dissolve for about 5 min. Then add 0.3 mL of 6M acetic acid aqueous solution to the glass tube, and seal after three freeze-evacuation-thawing cycles. At this point, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine and cyclooctasulfide is 1:3:5, and the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:18:63.

[0057] (2) The sealed tube was heated in a 130 °C forced-air drying oven for 4 days. The precipitate was collected by filtration and washed three times each with anhydrous THF and acetone. Then, it was purified by a Soxhlet extractor of tetrahydrofuran and acetone for 24 h. After vacuum drying, a solid powder was obtained, which is the azobenzene functionalized covalent organic framework material (i.e., Azo-COF). The yield of this example was 75.2%. PXRD test showed that the Azo-COF prepared in this example had good crystallinity, and its BET specific surface area was measured to be 389.17 m². 2 / g.

[0058] Example 3 A method for preparing an azobenzene-functionalized covalent organic framework material includes the following steps: (1) Add 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (30.9 mg, 0.05 mmol), 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine (72.9 mg, 0.20 mmol), cyclooctasulfide (102.6 mg, 0.40 mmol), dimethyl sulfoxide (150 μL), o-dichlorobenzene (570 μL), and n-butanol (2280 μL) to a heat-resistant Pyrex glass tube and sonicate to dissolve for about 5 min. Then add 0.3 mL of 6M acetic acid aqueous solution to the glass tube, and seal after three freeze-evacuation-thawing cycles. At this point, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine and cyclooctasulfide is 1:4:8, and the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:15:60.

[0059] (2) The sealed tube was heated in a 100 °C forced-air drying oven for 5 days. The precipitate was collected by filtration and washed three times each with anhydrous THF and acetone. Then, it was purified by a Soxhlet extractor of tetrahydrofuran and acetone for 24 h. After vacuum drying, a solid powder, namely Azo-COF, was obtained. The yield of this example was 68.6%. PXRD test showed that the Azo-COF prepared in this example was a semi-crystalline solid, and its BET specific surface area was measured to be 180.46 m². 2 / g.

[0060] Example 4 A method for preparing an azobenzene-functionalized covalent organic framework material includes the following steps: (1) Add 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (31.0 mg, 0.05 mmol), 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine (36.5 mg, 0.10 mmol), cyclooctasulfide (51.3 mg, 0.20 mmol), dimethyl sulfoxide (150 μL), o-dichlorobenzene (950 μL), and n-butanol (1900 μL) to a heat-resistant Pyrex glass tube and sonicate to dissolve for about 5 min. Then add 0.3 mL of 6M acetic acid aqueous solution to the glass tube, and seal after three freeze-evacuation-thawing cycles. At this point, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine and cyclooctasulfide is 1:2:4, and the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:25:50.

[0061] (2) The sealed tube was heated in a 150 °C forced-air drying oven for 3 days. The precipitate was collected by filtration and washed three times with anhydrous THF and acetone. Then, it was purified by a Soxhlet extractor of tetrahydrofuran and acetone for 24 h. After vacuum drying, a solid powder, namely Azo-COF, was obtained. The yield of this example was 70.2%. PXRD test showed that the Azo-COF prepared in this example was a semi-crystalline solid, and its BET specific surface area was measured to be 260.35 m². 2 / g.

[0062] Comparative Example 1 A method for preparing an azobenzene-functionalized covalent organic framework material includes the following steps: (1) Add 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (30.9 mg, 0.05 mmol), 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine (36.4 mg, 0.10 mmol), cyclooctasulfide (76.8 mg, 0.30 mmol), dimethyl sulfoxide (150 μL), o-dichlorobenzene (1425 μL), and n-butanol (1425 μL) to a heat-resistant Pyrex glass tube and sonicate to dissolve for about 5 min. Then add 0.3 mL of 6M acetic acid aqueous solution to the glass tube, and seal after three freeze-evacuation-thawing cycles. At this point, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine and cyclooctasulfide is 1:2:6, and the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:38:38.

[0063] (2) The sealed tube was heated in a 120°C forced-air drying oven for 4 days. The precipitate was collected by filtration and washed three times each with anhydrous tetrahydrofuran (THF) and acetone. Then, it was purified by a Soxhlet extractor of tetrahydrofuran and acetone for 24 hours. After vacuum drying, a solid powder was obtained, which is the azobenzene functionalized covalent organic framework material (i.e., Azo-COF). The yield of this example was 38.2%. PXRD test showed that the Azo-COF prepared in this example was an amorphous polymer and did not have crystallinity. Its BET specific surface area was measured to be 26.95 m². 2 / g.

[0064] Application Example 1 The Azo-COF prepared in Example 1 was combined with carbon nanotubes to form a composite material, and the electrochemical properties of the composite material were modulated using ultraviolet light.

[0065] The preparation method of Azo-COF / CNT composite material includes the following steps: Azo-COF (75 wt%) and carbon nanotubes (25 wt%) were dispersed and mixed in ethanol (the concentration of Azo-COF in ethanol was 1 mg / mL, and the concentration of carbon nanotubes in ethanol was approximately 0.33 mg / mL). After sonication for 5 min, a dispersion was obtained. The dispersion was then filtered and dried to obtain a composite material of Azo-COF and carbon nanotubes (Azo-COF / CNT).

[0066] The testing method for the effect of ultraviolet light on the electrochemical performance modulation of Azo-COF / CNT is as follows: Azo-COF / CNT solid powder was irradiated with 365 nm ultraviolet light for 30 min, and the ultraviolet absorption spectra of the solid sample before and after ultraviolet irradiation were measured to calculate its band gap energy. The conductivity of Azo-COF / CNT before and after ultraviolet irradiation was measured by the four-probe resistance method.

[0067] Preparation of the working electrode: Azo-COF / CNT, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 7:2:1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent was added and ground to prepare a uniform slurry. The slurry was uniformly coated onto copper foil and dried overnight at 50 °C. Afterward, the copper foil was cut into 8 mm diameter discs using a roller press and stored under vacuum for later use. The mass loading of Azo-COF / CNT was approximately 1.5 mg / cm². 2An Azo-COF / CNT electrode was used as the working electrode, a Li foil as the counter electrode, and a mixture of 1.0 M LiPF6 in ethylene carbonate / dimethyl carbonate (EC / DEC, volume ratio 1:1) and fluoroethylene carbonate (10 wt% fluoroethylene carbonate in the mixture) was used as the electrolyte. The button cell was then assembled in an argon-filled glove box. Cyclic voltammetry was performed to compare the CV curves before and after UV irradiation. The CV cycle curve of cis-Azo-COF / CNT at 1 mV / s was recorded, and finally, the contribution of capacitance to charge storage before and after UV irradiation was calculated.

[0068] Figure 10 (a) shows the change in band gap of Azo-COF / CNT before and after UV irradiation. Before UV irradiation, the band gap of trans-Azo-COF / CNT was 2.30 eV, and after UV irradiation, the band gap of cis-Azo-COF / CNT was 2.20 eV, which is significantly reduced. Figure 10 (b) shows the change in conductivity of Azo-COF / CNT before and after UV irradiation. The conductivity of Azo-COF was too low to be measured, so a conductivity of 0 S / m was used. Before UV irradiation, the conductivity of trans-Azo-COF / CNT was 2.02 S / m, indicating that compositing with carbon nanotubes can effectively improve the conductivity of Azo-COF. After UV irradiation, the conductivity of cis-Azo-COF / CNT was 11.56 S / m, indicating that the conductivity is light-tunable. These results indicate that cis-Azo-COF / CNT has a larger pore size, and the redox active sites such as C=N and N=N in the pores are fully exposed, which is more conducive to electron transport, leading to an increase in conductivity.

[0069] Figure 11 This study demonstrates the contribution of capacitance to charge storage in Azo-COF / CNTs before and after UV irradiation. The contributions of capacitance and diffusion to charge storage were calculated by scanning at different scan rates (1–10 mV / s). Before UV irradiation, the percentage of current contributed by capacitance was 56.0%, 66.3%, 73.6%, and 80.0% at scan rates of 1, 2, 5, and 10 mV / s, respectively. The percentage of capacitance contribution increased significantly with increasing scan rate, indicating that the lithium-ion storage process in Azo-COF / CNTs is dominated by a kinetically rapid pseudocapacitive process. After UV irradiation, the percentage of current contributed by capacitance was 79.5%, 80.5%, 83.3%, and 92.8% at scan rates of 1, 2, 5, and 10 mV / s, respectively, all significantly higher than before UV irradiation. This suggests that the redox active sites in cis-Azo-COF / CNTs are utilized more effectively, exhibiting favorable charge transfer kinetics. This is because UV irradiation opens the pores of Azo-COF, fully exposing redox active sites such as C=N and N=N within the pores, greatly accelerating the Li...+ The migration.

[0070] Figure 12 (a) shows the CV curves before and after UV irradiation. The effect of photoisomerization of azobenzene in Azo-COF / CNT on the electrochemical performance was analyzed using CV (scan rate 5 mV / s, voltage window 0.01–3.0 V) on a coin cell. The area under the CV curve of Azo-COF / CNT increased slightly after UV irradiation, indicating that the redox active sites of cis-azobenzene were utilized more effectively after UV irradiation. See also... Figure 12 As shown in (b), the CV modes of cis-Azo-COF / CNT almost overlap during cycling, indicating that cis-Azo-COF / CNT exhibits highly reversible redox reactivity and excellent cycling stability.

[0071] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An azobenzene-functionalized covalent organic framework material, characterized in that, The structural formula is as follows: ， The azophenyl group in the structural formula undergoes a trans-to-cis isomerization change under ultraviolet light.

2. The azobenzene functionalized covalent organic framework material as described in claim 1, characterized in that, The specific surface area of ​​the azobenzene functionalized covalent organic framework material changed by 12% to 20% before and after irradiation with 365nm ultraviolet light.

3. The azobenzene functionalized covalent organic framework material as described in claim 1, characterized in that, The azobenzene-functionalized covalent organic framework material exhibits a pore volume change rate of 15%–40% and a pore diameter change rate of 7%–10% before and after irradiation with 365 nm ultraviolet light.

4. A method for preparing the azobenzene functionalized covalent organic framework material as described in claim 1, characterized in that, Includes the following steps: 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine, elemental sulfur, and a mixed solvent were mixed evenly, and then heated under catalytic conditions in a sealed liquid nitrogen cryogenic vacuum environment. After post-treatment, the azobenzene functionalized covalent organic framework material was obtained. The mixed solvent is composed of dimethyl sulfoxide, o-dichlorobenzene and n-butanol.

5. The method for preparing the azobenzene functionalized covalent organic framework material as described in claim 4, characterized in that, In the mixed solvent, the volume ratio of dimethyl sulfoxide, o-dichlorobenzene and n-butanol is 4:15~25:50~63.

6. The method for preparing the azobenzene functionalized covalent organic framework material as described in claim 4, characterized in that, The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde, 2'-(phenylazo)-[1,1':4',1''-terphenyl]-4,4''-diamine, and elemental sulfur is 1:2~4:4~8.

7. The method for preparing the azobenzene functionalized covalent organic framework material as described in claim 4, characterized in that, The ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde to the mixed solvent is 0.015 mmol to 0.020 mmol: 1 mL.

8. The method for preparing the azobenzene functionalized covalent organic framework material as described in claim 4, characterized in that, The catalyst is an aqueous solution of acetic acid.

9. The method for preparing the azobenzene functionalized covalent organic framework material as described in claim 4, characterized in that, The reaction temperature for the sealed heating reaction is 100~150℃.

10. The method for preparing the azobenzene functionalized covalent organic framework material as described in claim 4, characterized in that, The reaction time for the sealed heating reaction is 3 to 5 days.

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